Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH₂ prepared by mechanical milling

We examined the catalytic effect of nanoparticle 3d-transition metals on hydrogen desorption (HD) properties of MgH₂ prepared by mechanical ball milling method. All the MgH₂ composites prepared by adding a small amount of nanoparticle Fe^nano, Co^nano, Ni ^nano, and Cu^nano metals and by ball milling for 2 h showed much better HD properties than the pure ball-milled MgH₂ itself. In particular, the 2 mol% Ni^nano-doped MgH₂ composite prepared by soft milling for a short milling time of 15 min under a slow milling revolution speed of 200 rpm shows the most superior hydrogen storage properties: A large amount of hydrogen (∼6.5 wt%) is desorbed in the temperature range from 150 to 250°C at a heating rate of 5°C/min under He gas flow with no partial pressure of hydrogen. The EDX micrographs corresponding to Mg and Ni elemental profiles indicated that nanoparticle Ni metals as catalyst homogeneously dispersed on the surface of MgH₂. In addition, it was confirmed that the product revealed good reversible hydriding/dehydriding cycles even at 150°C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH₂ could be understood by a modified first-order reaction model, in which the surface condition was taken into account.